1. Field of the Invention
This invention pertains to controlling internal combustion engines, and more particularly to apparatus for changing engine speed in response to changes in welding power requirements.
2. Description of the Prior Art
Internal combustion engines are an integral part of self-contained welding machines. It is known to equip such welding machines with controls that vary the engine speed based on the instantaneous demand for welding power. While welding is occurring, the engine governor sets the engine at a predetermined operating speed. For economic and environmental reasons, the control sets the engine at a lower idle speed during intervals when no welding is taking place.
A popular engine speed control on prior self-contained welding machines included a solenoid having its plunger connected to a governor arm of the engine. During periods of welding, the governor maintained the engine operating speed, such as 3700 revolutions per minute. When the control sensed that no welding had occurred for a predetermined time, such as 12 seconds, the control operated the solenoid to position the governor arm to decrease the engine speed to an idle speed, such as 2200 revolutions per minute.
The prior engine speed control included a small housing that was stationarily fastened to a solid surface on the welding machine. Screws passing through horizontally oriented slots in the housing walls held the solenoid in place with its plunger horizontal. The plunger was pinned to the engine governor arm. The housing slots enabled the solenoid to be adjusted horizontally relative to the housing, thereby adjusting the position of the engine governor arm to the desired idle speed. When the solenoid was at the proper location relative to the engine, it was firmly tightened in place with the screws through the housing walls. The screws also held a slotted cover on the housing. The cover overhung the solenoid plunger.
Although the prior engine speed control for self-contained welding machines has been successful in operation, it nevertheless had the characteristic of being rather difficult to initially adjust. The slots in the housing walls that allowed linear adjustment of the solenoid relative to the housing also enabled the solenoid to tilt about a horizontal axis. If the solenoid tilted such that the plunger was not aligned horizontally, the pin between the plunger and the engine idle arm could bind. If the misalignment was severe, the end of the plunger could contact the engine governor arm and possibly cause improper engine operation.
The overhanging cover aggravated the adjustment problem. Since the cover was held to the housing by the same screws that held the solenoid, the cover was in place over the solenoid as the solenoid was adjusted. Consequently, it was difficult for a worker to see the solenoid and its plunger while he adjusted the solenoid. Further, it was a tricky task to hold and align both the solenoid and the cover while simultaneously tightening the screws. Moreover, even if the solenoid and cover were properly adjusted initially, vibrations and relocations of the machine during normal use could have a tendency to work the screws loose. In severe cases, the solenoid plunger and governor arm could then bind, or the cover could tilt until its overhanging end contacted the solenoid plunger.
Another disadvantage of the engine speed control of prior self-contained welding machines concerned the solenoid wiring. At the assembly of the welding machine, a first wire was connected between the machine control circuit and the solenoid, and a second wire was connected between the solenoid and a ground. However, at the state of machine assembly when the solenoid was wired, the only practical ground available was a painted surface on the machine frame.